Effect of the combined application of fungal residue and chemical fertilizers on the mineralization of soil organic carbon in paddy fields

Improving soil quality, reducing waste, and mitigating climate change require an understanding of the balance between soil organic carbon (SOC) accumulation and depletion after the application of different quantities of fungal residue and chemical fertilizers. We evaluated the mineralized carbon (MC) content and mineralization rate (MR) after nine applications of chemical fertilizers (C) and fungal residue (F) in paddy fields, at rates of 0, 50, and 100%. A double exponential model was used to calculate the potential rates of MC and SOC turnover. The combined application of fungal residue and chemical fertilizers led to significantly higher MC and MR, by 24.97–100.05 and 24.36–98.07%, respectively, during 57 days of incubation than that of the control. The MC and MR values were highest with the C₅₀F₁₀₀ treatment. Simulations with the double exponential model showed that both the active SOC pools (C₁) and potential SOC mineralization flux C₁ + C₂ were highest with C₅₀F₁₀₀, and the MR constants, k₁ and k₂, were highest with C₁₀₀F₁₀₀. The potential SOC MR [(C₁ + C₂) / SOC] was highest with C₅₀F₁₀₀. The application of fungal residue and chemical fertilizers to paddy fields effectively alleviated soil acidification caused by chemical fertilizers and increased the nutrient content, MC, MR, C₁, and C₁ + C₂ of soils. However, the over-use of fungal residue or chemical fertilizers produces the reverse effects. Therefore, appropriate quantities of chemical fertilizers and fungal residue need to be applied to enhance the carbon sequestration capacity of soils while improving the MC and MR.